Inbound Links
This is a hypertext link to a page from another site, bringing traffic to that page. Inbound links are used to calculate link popularity.

Image Map
An image that has different clickable areas linked to different pages. Image maps can either be imbedded in the HTML code or called as an external file. Search engines usually have difficulty spidering image maps when they are included from external files.

Index
Plural: indices / indexes
The list of web pages stored and ranked by a search engine. Also known as a database.

Index file
A file created by a search indexer program, designed to store information in a format that makes fast retrieval possible.

Inktomi
A large database of web sites, started in 1996, that feeds results to somesearch engines. Inktomi also provides a range of other services, including content networking solutions, search solutions and wireless solutions.

Invisible Text
Text on a web page that is exactly or almost the same color as the background. The use of invisible text to load a page with keywords was once a popular SEO technique, but search engines can now detect invisible text and penalize sites that use it. Although there are examples of sites that use invisible text and "get away with it" on Google, the general consensus is that it is not worth the risk. The same results can usually be achieved by working the keywords into the visible body text.

Invisible Web
A popular collective name for documents of types that search engines do not typically index. Because they are not in any search engine database, they can be very difficult to find and are in a sense invisible. Recently a couple of specialized search engines have begun an attempt to make the invisible web more accessible.

IP address
Every Internet user and every server has a numeric address. Something like 123.45.67.890. IP addresses provide essential identification online. Domain names can be set up to have a unique IP address, something that is useful in SEO.